Numerous genetic diseases are caused by mutations in the genome. Several types of modifications have been found to be mutated in the genome: deletion of one or several base pairs, one or several mismatches in the sequence of the gene, insertion of one or several nucleotides, or repeat triplet reiteration and absence or duplication of a whole or part of a gene.
Genetic diseases caused by mismatches, deletion or insertion of one or several base pairs include cystic fibrosis, muscular dystrophy, sickle cell anemia, hemophilia, β-thalassemia, Fragile X syndrome.
RNA repair can be employed to repair genetic defects at the RNA level.
Oligonucleotides and complexes thereof have been employed as therapeutic molecules to repair DNA modifications (I Papaioannou, J P Simons, J S Owen Oligonucleotide-directed gene-editing technology: mechanisms and future prospects Expert Opin. Biol. Ther. (2012) 12(3):329-342). These oligomers can contain RNA and/or DNA nucleotides, or modified RNA or DNA nucleotides. They are employed to obtain site-specific repair of defective DNA. The repair was anticipated to occur through activation of endogenous DNA repair mechanisms after recognition of the introduced mismatch.
Triplex forming oligonucleotides also have been employed as sequence-specific tools for gene targeting. Triplex forming oligonucleotides bind in the major groove of double stranded DNA, with high affinity. Because of this characteristic, triplex forming oligonucleotides have been proposed as tools for the site specific corrections of targeted genes (Knauert et al., Hum Mol Genet. (2001) 10, 2243-2251; Richardson et al, Drug Target (2002) 10, 133-134; Thoung et al., (1993) Angewandte Chemie. Intl. Ed. Eng., 32, 666-690.). Current targeted gene repair methods are not very efficient, and/or have not been proven to work in living cells in situ, leaving space for another mechanism to repair gene defects.
Repair of defective genes at the RNA level has been reported. The specific repair of mRNA by a complex of duplexed oligonucleotides was e.g. employed to insert nucleotides in the ΔF508 CFTR mRNA in vitro. The mechanism through which this is mediated is postulated to be RNAse H-mediated degradation, followed by RNA repair. (P C Zamecnik, M K Raychowdhury, D R Tabatadze, H F Cantiello Reversal of cystic fibrosis phenotype in a cultured ΔF508 cystic fibrosis transmembrane conductance regulator cell line by oligonucleotide insertion Proc Natl Acad Sci 2004 101(21) 8150-8155; WO2005094370, oligonucleotide complex compositions and methods of use as gene alteration tools).